We propose an adiabatic time evolution (ATE) method for obtaining the ground state of a quantum many-electron system on a quantum circuit based on first quantization. As a striking feature of the ATE method, it consists of only unitary operations representing real-time evolution, which means that it does not require any ancillary qubits, nor controlled real-time evolution operators. Especially, we explored the first-quantized formalism of ATE method in this study since the implementation of first-quantized real-time evolution on quantum circuits is known to be efficient. However, when realizing the ATE quantum circuit in first-quantization formalism, obstacles are how to set the adiabatic Hamiltonian and how to prepare the corresponding initial ground state. We provide a way to prepare an antisymmetrized and nondegenerate initial ground state that is suitable as an input to an ATE circuit, which allows our ATE method to be applied to systems with any number of electrons. In addition, by considering a first-quantized Hamiltonian for quantum-mechanical electron system and classical nuclear system, we design a quantum circuit for optimal structure search based on ATE. Numerical simulations are demonstrated for simple systems, and it is confirmed that the ground state of the electronic system and optimal structure can be obtained by our method.

An alternative measure of information leakage for quantum encoding of classical data is defined. An adversary can access a single copy of the state of a quantum system that encodes some classical data and is interested in correctly guessing a general randomized or deterministic function of the data (e.g., a specific feature or attribute of the data in quantum machine learning) that is unknown to the security analyst. The resulting measure of information leakage, referred to as maximal quantum leakage, is the multiplicative increase of the probability of correctly guessing any function of the classical data upon observing measurements of the quantum state. Maximal quantum leakage is shown to satisfy the postprocessing inequality (i.e., applying a quantum channel reduces information leakage) and independence property (i.e., leakage is zero if the quantum state is independent of the classical data), which are fundamental properties required for privacy and security analysis. It also bounds accessible information. Effects of global and local depolarizing noise models on the maximal quantum leakage are established.

We calculate, via variational techniques, single- and two-photon Rydberg microwave transitions, as well as scalar and tensor polarizabilities of the sodium atom using the parametric one-electron valence potential, including the spin-orbit coupling. The trial function is expanded in a basis set of optimized Slater-type orbitals, resulting in highly accurate and converged eigenenergies up to $n=60$. We focus our studies on the microwave band 90–150 GHz due to its relevance to laser excitation in the Earth's upper-atmospheric sodium layer for wavelength-dependent radiometry and polarimetry, as precise microwave polarimetry in this band is an important source of systematic uncertainty in searches for signatures of primordial gravitational waves within the anisotropic polarization pattern of photons from the cosmic microwave background. We present the most efficient transition coefficients in this range, as well as the scalar and tensor polarizabilities compared with available experimental and theoretical data.

In atomic vapor cells, atoms collide with the inner surface, causing their spin to randomize on the walls. This wall-depolarizing effect can be diffusive and it becomes more pronounced in smaller vapor cells under high temperatures. In this work we investigate the polarization of optically pumped alkali-metal atoms in a millimeter-sized cell heated to $150{}^{\circ }\text{C}$. We consider two extreme boundary conditions, fully depolarizing and nondepolarizing boundaries, and we provide an analytical estimation of the polarization difference between them. In the nondepolarizing case, the pump beam's absorption is proportional to the average atomic polarization. However, for fully depolarizing walls, the absorption peak may correspond to a polarization minimum. To mitigate the wall effect, we propose reducing the pump beam's diameter while maintaining the pump power to prevent illumination of the cell wall and increase the pump intensity in the central area. This is crucial for compact vapor-cell devices where the laser frequency cannot be detuned since it is locked to the absorption peaks. Additionally, we analyze the wall-depolarizing effect on the performance of an alkali-metal atomic magnetometer operating in the spin-exchange relaxation-free regime. We show that the signal strength is highly limited by wall collisions and we provide an upper bound for it.

Quantum entanglement between distant massive mechanical oscillators has played a central role in building and engineering quantum devices for application in long-distance quantum communications, distributed quantum sensing, and synchronized quantum processing. Here we propose to control quantum entanglement of two spatially separated mechanical oscillators in a cascaded quantum system by applying two counterpropagating pump fields. In particular, we find that by adjusting the phase difference of pump lasers, quantum entanglement between such two mechanical oscillators can be significantly enhanced, together with improved robustness against environmental thermal noise. Our work opens up a well-accessible way to manipulate and protect mechanical entanglement, shedding light on a wide range of practical applications requiring robust purely quantum resources.

Quantum indistinguishability by path identity generates a new way of optical coherence, called “induced coherence.” The phenomenon, originally uncovered by Zou, Wang, and Mandel's experiment, is an emerging notion in modern quantum experiments with a wide range of implications. However, there has been controversy over its true quantum nature and whether the result can be emulated with classical light. We design a suitable contextuality test that can determine the conditions under which the setting produces distinguishing quantum predictions that cannot be described classically, namely, via the noncontextual hidden variable model.

Quantum state tomography (QST), the process through which the density matrix of a quantum system is characterized from measurements of specific observables, is a fundamental pillar in the fields of quantum information and computation. In this work, we propose a simple QST method to reconstruct the density matrix of two qubits encoded in the polarization and path degrees of freedom of a single photon, which can be realized with a single linear-optical setup. We demonstrate that the density matrix can be fully described in terms of the Stokes parameters related to the two possible paths of the photon, together with a quantum version of the two-point Stokes parameters introduced here. Our findings put forward photonic circuits for the investigation of the dynamics of open quantum systems.

We introduce a quantum charging distance as the minimal time that it takes to reach one state (charged state) from another state (depleted state) via a unitary evolution, assuming limits on the resources invested into the driving Hamiltonian. For pure states it is equal to the Bures angle, while for mixed states its computation leads to an optimization problem. Thus, we also derive easily computable bounds on this quantity. The charging distance tightens the known bound on the mean charging power of a quantum battery, it quantifies the quantum charging advantage, and it leads to an always achievable quantum speed limit. In contrast with other similar quantities, the charging distance does not depend on the eigenvalues of the density matrix, it depends only on the corresponding eigenspaces. This research formalizes and interprets quantum charging in a geometric way, and provides a measurable quantity that one can optimize to maximize the speed of charging of future quantum batteries.

The onset of retardation effects in atom-wall interactions is studied. It is shown that the transition range from the $1/z^3$ short-range (van der Waals) interaction to the $1/z^4$ long-range (Casimir) retarded interaction critically depends on the atomic properties and on the dielectric function of the material. For simple non-alkali-metal atoms (e.g., ground-state hydrogen and ground-state helium) interacting with typical dielectric materials such as intrinsic silicon, the transition to the retarded regime is shown to proceed at a distance of about 10 nm (200 Bohr radii). This is much shorter than typical characteristic absorption wavelengths of solids. Larger transition regimes are obtained for atoms with a large static polarizability such as metastable helium. We present a simple estimate for the critical distance, $z_{\mathrm{cr}}=137\sqrt{\alpha \left(0\right)/Z}$ atomic units, where $\alpha \left(0\right)$ is the static polarizability (expressed in atomic units) and $Z$ is the number of electrons of the atom.

Characteristic x-ray spectra offer insight into the structure and composition of atoms and molecules at a fundamental level where discrepancies in asymmetry, peak energy, and shape between theory and experiment motivate investigations. This work calculates highly convergent electron wavefunctions using the multiconfiguration Dirac-Hartree-Fock method and reveals the capability of recreating x-ray spectra from first principles, with eigenvalue convergence of order 0.1 eV and amplitude convergence of order 1–4%. The canonical $K\alpha$ and $K\beta$ transitions, $\left[1s\right]\to \left[2p\right]$ and $\left[1s\right]\to \left[2p\right]$, respectively, where square brackets denote hole states, are not sufficient to recreate major features present in the data. Shake-off satellites, where the transitions take place in the presence of a secondary $nl$ hole, are necessary to account for observed asymmetries. The probabilities for these shake-off events are determined and used to obtain ab initio satellite intensities. The Auger effect is considered for these satellite intensities through an Auger suppression factor. This work presents the full energy eigenvalue spectrum for several scandium transitions: $\left[1s^2\right]$ hypersatellites ($K{\alpha }^h$ and $K{\beta }^h$), the $n=2 K{\alpha }_{3,4}$ and $K\beta$ equivalent satellites, and double shake-off satellites. Calculations are compared with deconvolved experimental data using several fitting models which yield compelling goodness of fit ${\chi }_r^2=1.14$ for $K\alpha$ and ${\chi }_r^2=1.72$ for $K\beta$. The selected best model is chosen through the statistical $F$-test and this model is fitted with raw (not deconvolved) experimental data with ${\chi }_r^2=0.92$ ($K\alpha$) and ${\chi }_r^2=1.31$ ($K\beta$).

This study investigates the ultrafast fragmentation of ammonia clusters, ${\left({\mathrm{NH}}_3\right)}_n$ ($n=2$, 3, and 4), by using ion-ion multibody coincidence measurements after interaction with a strong femtosecond laser. Specifically, the Coulomb explosion and proton transfer channels in the dimer, as well as the Coulomb explosion of tri- and tetramers, are assigned. The kinetic energy release distributions and Newton plots of each channel are extracted and analyzed. To gain further insights into the dissociation process, an ab initio molecular dynamics simulation was performed to uncover the dissociation mechanism. In addition, the stretching of clusters during the Coulomb explosion was identified using classical trajectory calculation combined with the genetic algorithm. This combined experimental and theoretical study holds significant importance in improving the understanding of the ultrafast Coulomb explosion process in molecular clusters.

We report on the transport of a thermal cloud of ultracold cesium and rubidium atoms over about 37 cm in under 25 ms using an optical conveyor belt formed by two counterpropagating beams with a controllable frequency difference that generate a movable optical lattice. By carefully selecting the waists and focus positions, we are able to use two static Gaussian beams for the transport, avoiding the need for a Bessel beam or variable-focus lenses. We characterize the transport efficiency for both species, including a comparison of different transport trajectories, gaining insight into the loss mechanisms and finding the minimum jerk trajectory to be optimum. Using the optimized parameters, we are able to transport up to $7\times {10}^6$ cesium or rubidium atoms with an efficiency up to 75%. To demonstrate the viability of our transport scheme for experiments employing quantum gas microscopy, we produce Bose-Einstein condensates of either species after transport and present measurements of the simultaneous transport of both species.

It is well known that when two or more quantum measurements suffer from imperfections they may lose their incompatibility. For a quantum system of finite dimension $d$ we study the incompatibility of all projective measurements subjected to white noise and loss. We derive a necessary and sufficient condition for this set of measurements to become compatible in terms of their visibility $p$ and efficiency $\eta$.

Quantum simulations of many-body systems in materials science and chemistry are promising application areas for quantum computers. However, the limited scale and coherence of near-term quantum processors pose a significant obstacle to realizing this potential. Here, we theoretically outline how a single-mode circuit quantum electrodynamics device, consisting of a transmon qubit coupled to a long-lived cavity mode, can be used to simulate the ground state of a highly entangled quantum many-body spin chain. We exploit recently developed methods for implementing quantum operations to sequentially build up a matrix product state (MPS) representation of a many-body state. This approach reuses the transmon qubit to read out the state of each spin in the chain and exploits the large state space of the cavity as a quantum memory encoding intersite correlations and entanglement. We show, through simulation, that analog (pulse-level) control schemes can accurately prepare a known MPS representation of a quantum critical spin chain in significantly less time than digital (gate-based) methods, thereby reducing the exposure to decoherence. We then explore this analog-control approach for the variational preparation of an unknown ground state. We demonstrate that the large state space of the cavity can be used to replace multiple qubits in a qubit-only architecture, and could therefore simplify the design of quantum processors for materials simulation. We explore the practical limitations of realistic noise and decoherence and discuss avenues for scaling this approach to more complex problems that challenge classical computational methods.

We consider the mean-field vortex solutions and their stability within a two-component Bose-Einstein condensate in the immiscible limit. A variational approach is employed to study a system consisting of a majority component which contains a single quantized vortex and a minority component which fills the vortex core. We show that a super-Gaussian function is a good approximation of the two-component vortex solution for a range of atom numbers of the infilling component by comparing the variational solutions to the full numerical solutions of the coupled Gross-Pitaevskii equations. We subsequently examine the stability of the vortex solutions by perturbing the infilling component away from the center of the vortex core, thereby demonstrating their stability to small perturbations. Finally, we consider the dynamics of infilled vortices.

We present an efficient cooling scheme for fermionic ${}^{40}\mathrm{K}$ atoms, using laser light red and blue detuned with respect to the D2 and D1 principle fluorescence lines, respectively. The cooling scheme is found to significantly increase the saturation level for loading of a ${}^{40}\mathrm{K}$ magneto-optical trap (MOT), resulting in increased atom numbers or decreased cycle times. While the attainable ${}^{40}\mathrm{K}$ atom number is approximately doubled if exclusively ${}^{40}\mathrm{K}$ atoms are cooled, the scheme is particularly powerful for dual-species MOTs, for example, if ${}^{40}\mathrm{K}$ and ${}^{87}\mathrm{Rb}$ atoms are cooled simultaneously in the same MOT configuration. The typical atom losses due to light-assisted heteronuclear collisions between ${}^{40}\mathrm{K}$ and ${}^{87}\mathrm{Rb}$ seem to be reduced, giving rise to a threefold improvement of the ${}^{40}\mathrm{K}$ atom number as compared to that in a conventional dual-species MOT, operating merely with D2 light. Our scheme can be a useful extension to most dual-species experiments, aiming to reach simultaneous degeneracy of both species.

In this paper, we investigate the characteristics of transverse spin and energy flow in Kerker scattering by a high refractive-index nanosphere based on the rigorous Mie scattering theory. It is found that the spin is quasi-transverse to the direction of energy flow everywhere in Kerker scattering and the magnitude of transverse spin is much larger than that in Rayleigh scattering due to the phase shift between scattered light of electric and magnetic dipoles. For the incidence of a linearly polarized plane wave, the transverse spin predominantly determines the direction of energy flow due to the spin-momentum locking effect in the near field. In the far field, the curl relationship between the energy flow and spin angular momentum density is validated analogously to structured guided waves. These findings help deepen understandings of unidirectional scattering and will be beneficial for the design of photonic nanoantennas.

In a recent paper [Phys. Rev. A 105, 042220 (2022)], Daley et al. claim that some superdeterministic models are disfavored relative to standard quantum mechanics because such models overfit the statistics of a Bell-type experiment which the authors conducted. We add to the discussion by providing additional context about how few superdeterministic models fall into the category they analyze, and by emphasizing that overfitting, while better as a measure of fine-tuning than other measures given in the literature, does not necessarily indicate a model is universally bad.

We examine two conditions that can be used to detect bipartite entanglement, and show that they can be used to provide lower bounds on the negativity of states. We begin with two-qubit states, and then show how what was done there can be extended to more general states. The resulting bounds are then studied by means of a number of examples. We also show that if one has some knowledge of the Schmidt vectors of a state, better bounds can be found.